The Face of Immortality?

They're as long as an eyelash and live in a pond. They attach themselves to pebbles and feed on insect larvae and tiny shrimp. They might also be immortal.

Or so says Daniel Martinez, a scientist at Pomona College who has studied these tentacled little critters for years. Since the early 1900s, people who'd worked with hydra claimed that the animals were immortal. “I didn't believe it,” says Martinez. “So I set out to prove them wrong.”

Sounds simple enough. If hydra were not immortal, all Martinez would have to do is stick some in a tank and then watch 'em die. So he did. But they didn't. Die, that is. At least not in the numbers that Martinez expected. Because hydra are so tiny—and start reproducing so early in life—Martinez predicted that they wouldn't last more than a month or two. Four years later, only a couple had croaked, meaning that most of the hydra had already survived more than 20 times as long as they should have.

What's more, these oldsters seemed “as good as new.” They were healthy, made babies, and were no more likely to die than the youngsters, says Martinez. So hydra, it seems, show no signs of aging.

But that doesn't make them immortal, says Rich Miller of the University of Michigan: “A lack of aging is not the same thing as immortality.” Imagine, for example, a population in which half of the animals die every minute, regardless of how old they are. The creatures won't appear to age—young ones will snuff it as often as the oldies. But, says Miller, “unless the population is large enough to fill the universe, there won't be any left by next Thursday.” Which hardly seems like a shining example of immortality.

The reason that hydra live so long and stay so youthful is that the little guys are essentially “a bag of stem cells,” says Martinez. Hydra can use these all-purpose cells to continuously rebuild their bodies.

As for their immortality, Martinez essentially agrees with Miller. “Maybe hydra are immortal,” he says. “But I wouldn't bet my life on it.”

Vocabulary

immortal: Living or lasting forever.

stem cell: An unspecialized cell that gives rise to a specific specialized cell, such as a blood cell.

Activity

What is strange about the way in which a hydra ages?[anno: The hydra's cells do not appear to age.]

You have read about certain plants that have life cycles that are hundreds of years long. A few plants even live to be thousands of years old, such as the giant sequoia and the creosote bush. Why might certain plants be better suited than animals to have such long life spans? What might be the benefit to studying plants that have such long life spans? Write a few sentences explaining what the benefits might be to studying long-lived plants.[anno: Answers will vary but could include that studying plants with a long life cycle might benefit us in learning about how certain organisms resist disease and environmental changes.]